A COMPARATIVE STUDY ON THE TRIBOLOGICAL BEHAVIOR OF NEW AND USED 10W-40 ENGINE OIL APPLIED IN GASOLINE AND DIESEL ENGINES

Abstract

This study presents a comparative analysis of the tribological behaviour of new and used SAE 10W-40 engine oil, collected from gasoline and diesel passenger car engines and tested under cold-start conditions. The investigation examined the influence of oil aging and engine type on viscosity, friction, and wear. Block-on-disc experiments were performed using aluminium (EN AW-6060) against hardened steel (EN 25CrMo4) following ASTM G77 procedures. The results showed that used oils exhibited lower coefficients of friction and smaller wear scars compared to new oil. The diesel-derived sample achieved the best performance, with the lowest steady-state friction and wear volume, likely due to degradation products and fuel residues that enhanced boundary lubrication. Although used oils displayed improved short-term tribological behaviour, their long-term performance in actual engines is limited by oxidation, contamination, and corrosiveness. These findings provide insights into lubricant degradation and may support the optimization of oil-change intervals and the development of improved multigrade oils.